One million people across three Yemeni cities are at risk of a renewed cholera outbreak and other water-borne diseases following the closing of airports and sea ports by a Saudi-led coalition fighting Yemen's Shiite rebels, an international aid group said on Friday.

The International Committee of the Red Cross said in a statement that the cities of Hodeida, Saada and Taiz were not able to provide clean water in recent days due to a lack of fuel.

"Close to one million people are now deprived of clean water and sanitation in crowded urban environments in a country slowly emerging from the worst cholera outbreak in modern times," said Alexander Faite, head of the Red Cross delegation in the war-ravaged nation.

The Red Cross said other major urban cities, including the capital Sanaa, will find themselves in the same situation in less than two weeks unless imports of essential goods resume immediately.

The U.S.-backed coalition imposed a land, sea and air blockade on November 6th after a missile attack by rebels targeted the Saudi capital Riyadh. Saudi Arabia said Monday the coalition would lift the blockade after widespread international criticism.

U.N. spokesman Stephane Dujarric said Guterres welcomed the reopening of the port in the city of Aden, however he said this "will not meet the needs of 28 million Yemenis."

People inspect the rubble of houses destroyed by Saudi-led airstrikes in Sanaa, Yemen, on Friday, Aug. 25, 2017.

Suspected airstrikes by the Saudi-led coalition killed at least 21 people on Friday in the country's west and northwest, said Yemeni security officials and witnesses.

One airstrike hit a bus in el-Zaher district in the western province of Hodeida, killing six civilians, they said. At least 15 people were killed in another airstrike on a market in Yemen's northwestern Hajja province, controlled by the Shiite rebels, the officials and witnesses added.

The officials and witnesses spoke on condition of anonymity because they are not authorized to brief reporters or for fear of reprisals.

There was no immediate comment from the coalition.

Over the past two years, more than 10,000 people have been killed and 3 million displaced in the coalition's air campaign. With the country in a stalemate war, cholera began to rear its ugly head in October 2016, but the epidemic escalated rapidly in April. The fighting has damaged infrastructure and caused shortages of medicine and pushed the Arab world's poorest country to the brink of famine.